Dilactone chromogenic compounds, preparation thereof, and pressure-sensitive copy systems employing same

ABSTRACT

WHEREIN R represents an alkyl group, an aryl group, an aralkyl group, an acyl group or an aroyl group; and X represents a hydrogen atom, a halogen atom, an alkyl group or a nitro group. The dilactone compounds are produced from precursor compounds that are formed by reacting pyromellitic dianhydride with a resorcinol having at least the fourth or the sixth position unsubstituted, in the presence of a dehydrating agent to form xanthyl derivatives of isophthalic and terephthalic acid. These precursors are then further reacted to form the dilactones. The dilactones are used in pressure-sensitive copy systems comprising a support bearing microcapsules containing the dilactones, alone, or in combination with other chromogenic materials.   AND   A substantially colorless dilactone chromogenic material having the structural formula

United States Patent [19] Vincent et a1.

[ DILACTONE CHROMOGENIC COMPOUNDS, PREPARATION THEREOF, ANDPRESSURE-SENSITIVE COPY SYSTEMS EMPLOYING SAME [75] Inventors: David N.Vincent, Glenview; Cheng Hsiung Chang, Chicago, both of I11. [73]Assignee: Champion International Corporation, New York, NY.

[22] Filed: Feb. 5, 1973 [21]. Appl. No.: 329,293

[52] 11.8. C1 117/36.2, 117/368, 260/335, 260/3433 [51] Int. Cl. B4lc1/06 [58] Field of Search 260/335, 343.3; 117/362, 117/368 [56]References Cited UNITED STATES PATENTS 643,37 1 2/ l 900 Brack 260/3 362,844,596 7/1958 Wheeler et a1. 260/3433 2,912,440 11/1959 Wheeler etal. 260/3433 3,244,548 4/ 1 966 Sullivan l 1 7/ 36.2 3,418,250 12/1968Vassiliades 117/36.2 X 3,418,656 12/1968 Vassiliades 117/362 X 3 ,663 ,57 1 5/ 1 972 Kimura et a1. 260/3 3 5 Primary Examiner-Thomas J. Herbert,Jr. Attorney, Agent, or Firm-Roylance, Abrams, Berdo & Kaul [5 7]ABSTRACT A substantially colorless dilactone chromogenic material havingthe structural formula [4 June 25, 1974 and wherein R represents analkyl group, an aryl group, an aralkyl group, an acyl group or an aroylgroup; and X represents a hydrogen atom, a halogen atom, an

alkyl group or a nitro group. The dilactone compounds are produced fromprecursor compounds that are formed by reacting pyromellitic dianhydridewith a resorcinol having at least the fourth or the sixth positionunsubstituted, in the presence of a dehydrating agent to form xanthylderivatives of isophthalic and terephthalic acid. These precursors arethen further reacted to form the dilactones. The dilactones are used inpressure-sensitive copy systems comprising a support bearingmicrocapsules containing the dilactones, alone, or in combination withother chromogenic materials.

12 Claims, No Drawings DILACTONE CHROMOGENIC COMPOUNDS, PREPARATIONTHEREOF, AND PRESSURE-SENSITIVE COPY SYSTEMS EMPLOYING SAME Thisinvention relates to chromogenic compounds, precursors for suchcompounds, the production of such compounds and to the use of suchcompounds in pressure-sensitive record material. More particularly, thisinvention relates to substantially colorless, dilactone chromogeniccompounds which are converted to a yellow color when placed in reactivecontact with Lewis acid materials, such as in a pressure-sensitive copysystern.

Numerous marking systems have been suggested which improve localizedcontact between a chromogenic compound and a color-developing substancein areas where a colored marking is desired. Pressuresensitivemark-forming systems are described, for example, in US. Pat. Nos.3,4l8,656 and 3,418,250 to A.E. Vassiliades. These patents describe amarking system wherein a substantially colorless chromogenic substanceis incorporated in minute oil droplets which are disposed within andthus form the core of pressurerupturable microcapsules. Themicrocapsules are coated onto a substrate which may be utilized adjacenta receiving sheet that is coated with an acidic material, such as aLewis acid-treated clay. Upon application of localized pressure, themicrocapsules are ruptured and the colorless chromogenic substance isreleased and reacts with the electron acceptor to provide a distinctivemark.

Various chromogenic compounds have been proposed for use in such markingsystems. Previously proposed chromogenic compounds include, for example,the rhodamine dilactones. Certain difficulties are experienced withparticular dilactones that have been previously suggested. For example,certain of the rhodamine dilactones have a tendency towards prematureopening of the lacetone rings causing premature coloration by moisture,for example, present in the atmosphere. Thus, such water sensitivityprevents a successful utilization of the chromogenic compounds in copysystems where the compounds must remain substantially colorless untilthe microcapsules containing the chromogenic materials are ruptured.

In accordance with the present invention, there is providedsubstantially colorless, chromogenic compounds having the structuralformula R represents an alkyl group, an aryl group, an aralkyl group, anacyl group or an aroyl group; and

X represents a hydrogen atom, a halogen atom, an

alkyl group or a nitro group.

The colorless dilactones of the present invention can be converted toyellow colored markings upon reaction with Lewis acid materials.Significantly, the dilactone compounds of the present invention areessentially insoluble in water, and thus may be easily encapsulated bydispersing the chromogenic substance in an oily solvent and suspendingthe resultant material in the form of microscopic droplets in anoil-in-water emulsion without premature coloration of the dyeintermediate. In addition, once the present chromogenic compounds areencapsulated, they are insensitive to moisture present in the atmosphereand thus may be stored until use without premature coloration. Moreover,dilactones of the present invention may be added to conventional blueimaging systems which contain, for example, Crystal Violet Lactone andBenzoyl Leuco Methylene Blue and thus provide improved blue images thatare readily reproducible by xerographic processes. Still further, blackimages may be. formed by combining the present dilactones with otherchromogenic materials as will be hereinafter illustrated.

Preferably, the dilactone compounds of the present invention have thestructural formulae (1) and (ll) wherein:

R represents a lower alkyl group containing from one to four carbonatoms, e.g. methyl, ethyl, propyl, butyl, an aryl group, e.g. phenyl,tolyl, etc., an aralkyl group, e.g. benzyl, phenethyl, etc., a loweracyl group, e.g. acetyl, butyryl, etc. or an aroyl group, e.g. benzoyl,etc., and

X represents a hydrogen atom, a chlorine or bromine atom, an alkyl groupcontaining from one to 20 carbon atoms, e.g. methyl, propyl, dodecane,eicosane, or a nitro group.

Examples of such compounds include:

trans 3 ,7-bis[ 3 ,6-dimethoxy-9 '-spiroxanthyl pyromellitide,

cis 3,5-bis[3,6'-dimethoxy-9'-spiroxanthy1lpyromellitide,

trans 3 ,7-bis[ 4' ,5 -dimethyl-3 ,6-dimethoxy-9 spiroxanthyl]pyromellitide,

cis 3,5-bis[4,5'-dimethyl-3,6,-dimethoxy-9- spiroxanthyl] pyromellitide,

trans 3,7-bis[2',7'-dichloro-3,6'-dimethoxy-9'- spiroxanthyl]pyromellitide,

cis 3,5-bis[2,7'-dichloro-3,6-dimethoxy-9'- spiroxanthyl] pyromellitide,

cis 3,5-bis[3',6'-diacetoxy-9'-spiroxanthyllpyromellitide,

trans 3,7-bis[3,6'-diacetoxy-9'-spiroxanthyl]- pyromellitide,

cis 3,5-bis[3,6'-dibutyroxy-9'-spiroxanthyl]- pyromellitide,

trans 3,7-bis[3,6'-dibutyroxy-9'-spiroxanthyl]- pyromellitide,

cis 3,5-bis[3,6-dibenzyloxy-9-spiroxanthyl]- pyromellitide,

trans 3,7-bis[3,6-dibenzyloxy-9'-spiroxanthyl]- pyromellitide,

trans 3 ,7-bis[ 3 ',6'-dibenzoxy-9 -spiroxanthyl pyromellitide,

cis 3,5-bis[3,6-dibenzoxy-9-spiroxanthyl]pyromellitide, and the like.

According to another aspect of the present invention, dilactoneprecursor compounds are produced by reacting pyromellitic dianhydridewith a resorcinol, which has at least the fourth or sixth positionunsubstituted, in the presence of a dehydrating agent to form xanthylderivatives of isophthalic and terephthalic acid as folcinol, 4-n-propylresorcinol, S-n-pentyl resorcinol, 4-ndodecyl resorcinol, 4-chlororesorcinol and the like.

Suitable dehydrating agents include, for example, anhydrous zincchloride, boron trichloride etherate, and the like. The formation of thexanthyl derivatives of isophthalic and terephthalic acid as shown above,may be conducted under any suitable conditions. For example, thisreaction takes place readily at elevated temperatures of between about180 and about 250C. without solvents for a period of time between about1 and about 5 hours.

The reaction can also be carried out in a solvent in which both of thereactants are either soluble or are at least partially soluble.Preferably, the solvents have boiling points within the range of 100 to175C, permitting the reaction to be carried out under reflux conditions.Suitable solvents include toluene, xylene, and the like, which solventsare well-known to those skilled in the art.

The dilactone precursors may be converted to the dilactone chromogeniccompounds by various techniques. According to a further aspect to theinvention,

trans HO X the hydroxyl groups contained in each precursor molecule canbe alkylated by any standard alkylation procedure as shown by thefollowing reaction for the cis and trans isomers:

ER 0 0R no 0 HO X The alkylation of the hydroxyl groups in the foregoingreactions involves the substitution of an alkyl group, an aryl group oran aralkyl group for the hydrogen of each hydroxyl group. Suchalkylation may be readily accomplished using a suitable alkylatingagent, such as, for example, a dialkyl sulfate, e.g., dimethyl sulfate,diethyl sulfate, etc. diazomethane, benzyl or phenyl halides, such asbenzyl chloride or monobromobenzene, etc. The alkylated products arethen saponified followed by acidifcation to form the desired cis andtrans dilactone chromogenic compounds.

alkylation Alternatively, the dilactone precursors, i.e., the xanthenylderivatives of isophthalic and terephthalic acid can be reacted with asuitable esterifying agent to form esterified dilactones. Thus, theprecursors may be reacted with a suitable acylation agent, such asacetic anhydride, butyric anhydride, acetyl chloride, benzoylchloride,benzoic anhydride, or the like. For example, employing acetic anhydrideas the acylation agent, the

following reaction takes place, for the cis isomer under refluxconditions According to still another aspect of the present invention,the dilactone compounds are employed in pressure-sensitive copy systems.Thus, the dilactone chromogenic compounds are incorporated into minuteoily droplets and encapsulated by any suitable process, such as thosedescribed in US. Pat. Nos. 3,418,250 and 3,418,565, which patents arehereby incorporated by reference. The microcapsules may be coated ontoor incorporated into a web or substrate, such as paper, and utilized inany type of pressure-sensitive copy system whereby the microcapsules areruptured under localized pressure to release the dilactones for contactwith an acidic co-reactant to provide a colored image. Thus, themicrocapsule-bearing substrate may comprise a single sheet, wherein themicrocapsules containing the dilactone and the acidic coreactant, suchas a suitable Lewis acid are coated onto a single substrate. Such systemis usually referred to as a self-contained" or autogenous system, sincethe colorless chromogenic material and the acid co-reactant are presenton the same substrate. Alternatively, the microcapsules containing thedilactones of the present invention may be coated onto or incorporatedinto a substrate which is used in combination with another sheet orsubstrate which contains the acidic coreactant. This system is normallyreferred to as a transfer system and the rupture of the microcapsulesresults in a transfer of the dilactone chromogen from themicrocapsule-coated sheet to an acid-coated sheet upon which a coloredmark is provided. The colorless dilactones of the present invention maybe utilized in any pressure-sensitive system where they are isolatedfrom an acidic coreactant prior to the formation of the desired coloredmarking. Any of the well-known acidic materials including bentonite,kaolin, acidic clays, talc, aluminum silicate, calcium citrate, metaloxides, metal chlorides, or the like may be utilized as the acidiccoreactant for the present dilactones.

As previously mentioned, the dilactones of the present invention providea yellow color upon contact with a Lewis acid material. However, thedilactones may be used in combination with other colorless chromogeniccompounds. Thus, for example, the present dilactones may be used toimprove a conventional blue imaging system, such as those comprisingCrystal Violet Lactone and Benzoyl Leuco Methylene Blue. The addition ofthe present dilactones to such systems improve the xeroxability of theresulting images. Similarly, the dilactones of the present invention maybe combined with still other colorless chromogenic compounds to provideblack images having improved xerographic reproduction qualities.

Any suitable amount of the dilactone chromogenic compounds of thepresent invention may be employed in the formation of microcapsules foruse in pressuresensitive systems. For example, between about 0.2 andabout 2.0 parts by weight of the dilactone may be employed for each 100parts by weight of the oily material which forms the core of themicrocapsule. Preferably, between about 0.6 and about 1.5 parts byweight of the dilactone per 100 parts by weight of the oily corematerial may be suitably employed. Larger amounts of the dilactone maybe utilized, if desired. However, large amounts are normally notnecessary since the greater quantities do not provide a correspondinglygreater intensity of color and, of course, the use of such largeramounts is economically undesirable. As previously indicated, when thedilactones are combined with blue imaging dye substances, such asCrystal Violet Lactone and Benzoyl Leuco Methylene Blue, or the like,the resultant image has been found to be better reproducible by normallyblue insensitive copying methods, such as the xerographic methods now inuse. This can be accomplished without materially modifying the visibleblue color of the resultant image. Thus, when dilactones of the presentinvention are combined with other chromogenic materials, it is preferredto use between about 0.1 and about 0.8 parts by weight of the dilactonewith about 1.5 to about 3.5 parts by weight of the blue image dyesubstance, all based upon 100 parts by weight of the oily material whichwill form the core of the microcapsules. If desired, additional amountsof the present lactone chromogenic materials may be added to give agreenish hue to the resultant colored image.

The invention will be further illustrated by the following examples. Thepercentages are by weight unless otherwise specified.

EXAMPLE 1 A mixture of 13.1 grams of pyromellitic dianhydride, 26.4grams of resorcinol, and 18 grams of boron trifluoride etherate in 300milliliters of dry xylene is refluxed for 3 hours. Near the end of thereflux, a brownish insoluble mass is formed and collected by filtration.Recrystallization from acetone-water in the ratio of 1:5 yields 20.8grams of xanthyl derivatives of isophthalic acid and terephthalic acid.

Twenty grams of anhydrous sodium carbonate are added to a solution of 20grams of the formed acids in 400 milliliters of anhydrous acetone. Themixture is brought to boiling and 40 grams of dimethyl sulfate are addedslowly. During the two hours reflux, a 20 percent methanolic potassiumhydroxide solution is used to keep the solution at pH 8. The solution iscooled, filtered, and neutralized with acetic acid. Upon the addition ofwater, a lightly yellowish precipitate is obtained. The infraredspectrum of the dried sample shows no hydroxyl groups.

The product is a mixture of dimethyl 4,6-bis[9'-(3',6',9-trimethoxy)xanthyl]isophthalate and dimethyl2,5-[9'-(3',6,9'-trimethoxy)xanthyllterephthalate.

The esters are further hydrolyzed with a 20 percent methanolic potassiumhydroxide solution at refluxing temperature for 2 hours at a pH greaterthan 13. The solution is then cooled, neutralized with acetic acid, andextracted with toluene. An almost colorless solid is obtained after theremoval of the toluene. Successive recrystallizations from acetoneresult in the separation of two isomeric color-formers. From theprecipitate, there isobtained 5.8 grams of trans 3,7-bis[3',6-dimethoxy-9-spiroxanthyl]pyromellitide, having a melting point of 362C,and an absorptive maximum in percent acetic acid at 441 mu. From themother 'Iiqiibi,4.0 grams of cis 3,5-bis[3',6'-dimethoxy-9'-spiroxanthyl]pyromellitide are obtained having an absorptive maximum in95 percent acetic acid at 442 my. and a melting point of 320C.

EXAMPLE 2 The procedure described in Example 1 is repeated, except thatresorcinol is replaced by an equivalent amount of a substitutedresorcinol. Thus, 2-methyl resorcinol is utilized to form trans3,7-bis[4,5-dimethyl- 9 3',6'-dimethoxy-9'-spiroxanthyl]pyromellitideand cis3,5-bis[4',5'-dimethyl-3',6-dimethoxy-9'-spiroxanthyl]pyromellitide,while 4 chlororesorcinol is employed to form trans3,7-bis[2',7'-dichloro-3',6-

'dimethoxy-9-spiroxanthyl]pyromellitide and cis 3,5-

bis[2',7'-dichloro-3,6'-dimethoxy-9'-spiroxanthyl]- pyromellitide.

EXAMPLE 3 The benzyloxy derivative is formed by following the procedureof Example 1, except that instead of using dimethyl sulfate, anequivalent amount of benzyl chloride in aqueous sodium hydroxide isadded to the hydroxy acid precursor solution. The cis and trans bis[3',- 6-dibenzyloxy-9-spiroxanthyl] pyromellitides are formed.

EXAMPLE 4 EXAMPLE 5 The procedure of Example 4 is repeated with theexception that butyric anhydride is used instead of acetic anhydride.Recrystallization from benzene-petroleum ether yields 5.5 grams of cis3,5-bis[3',6'-dibutyroxy- 9'-spiroxanthyl] pyromellitide and its transisomer having a melting point of 295C.

EXAMPLE 6 The procedure of Example 4 is followed with the exception that100 milliliters of benzoyl chloride are substituted for the aceticanhydride. The mixture is heated at a temperature of 140-l45C. for aperiod of 3 hours; About 50 milliliters of benzoyl chloride are removedunder reduced pressure. Petroleum ether is added to the cooled residueto precipitate out the prodnot and dissolve the unreacted benzoylchloride. The resulting insoluble material is boiled in water forminutes and then recrystallized from acetone yielding 63 grams of cis3,5-bis[3',6-dibenzoxy-9'- spiroxanthyl] pyromellitide and its transisomer having a melting point of 319323C.

EXAMPLE 7 Following the general microencapsulation procedure describedin U.S. Pat. No. 3,418,656, microcapsules are prepared containing thedilactone color chromogenic compounds prepared in Example 1, above.Thus, an oily mixture is formed containing one part by weight of eachisomeric dilactone formed in Example 1, 51 parts of coconut oil and 34parts of a partially hydroge nated terphenyl (specific gravity 1.005,flash point 345F. and pour point 28C. commercially available fromMonsanto Chemical Company as HB40). The oily mixture is emulsified in500 parts of a 6 percent by weight aqueous solution of methyl cellulose.The emulsion is maintained under continuous agi- 10 tation and 20 partsby weight of a B-stage ureaformaldehyde resin are added to the emulsion.The resulting amicrocapsules are then coated onto a sheet of paper.

The coated paper is then brought into contact with an acidic clay-coatedsheet, and localized pressure is applied with the stylus of a typewriterto rupture the capsules and release the dilactones for reaction with theclay-coated sheet. A yellow mark instantly develops on the clay-coatedsheet.

EXAMPLE 8 lsomeric mixtures of the chromogenic compound formed inExamples 2 and 3 are microencapsulated and coated onto sheets of paperin the manner described in Example 7. When each of the coated papers isbrought into contact with a clay-coated sheet, respectively, andlocalized pressure applied by means of a typewriter, a yellow markinstantly develops on each of the claycoated sheets.

EXAMPLE 9 The procedure of Example 7 is repeated, with the exceptionthat instead of utilizing the dilactone chromogenic compounds, alone,mixtures of 2.1 parts of Crystal Violet Lactone and 1.8 parts of BenzoylLeuco Methylene Blue are combined with 0.3 part of a mixture of trans3,7-bis[3',6'-dimethoxy-9'-spiroxanthyl]- pyromellitide and cis3,5-bis[3',6'-dimethoxy-9- spiroxanthyl]pyromellitide.

A blue colored image develops on the clay-coated paper upon rupture ofthe microcapsules, and the resulting image is readily duplicated by axerographic copying machine.

EXAMPLE 10 The procedure of Example 7 isfollowed, while utilizing amixture of chromogenic compounds including 1.2 parts by weight of amixture of trans 3,7-bis[3',6'- dimethoxy-9'-spiroxanthyl]pyromellitideand cis 3,5- bis[ 3 ',6 -dimethoxy-9 '-spiroxanthyl ]pyromellitide, 0.02part by weight of 7,7-bis(3-diethylaminofluoran), 0.8 part by weight of7,7'-isopropylidene-bis(3- diethylaminofiuoran), 1.3 parts by weight ofCrystal Violet Lactone, and 0.6 part by weight of Benzoyl LeucoMethylene Blue.

The preparation of the bisfluorans is disclosed in copending U.S. Patentapplication Ser. No. 329,294, filed Feb. 5, 1973 entitled BisfluoranChromogenic Compounds, Preparation Thereof, and Pressure-Sensitive CopySystems Employing Same.

A black image, which is capable of being xerographically reproduced, isimmediately formed on the claycoated paper upon rupture of the capsulesby the application of localized pressure using a typewriter stylus. Theresulting image has good reproducibility using a Xerox duplicatingmachine.

This invention has been described in considerable detail with particularreference to preferred embodiments, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described in the appended claims.

What is claimed is:

l. A pressure-sensitive copy system comprising a substrate bearingpressure-rupturable microcapsules, said microcapsules containing atleast one chromogenic compound having the formula \C/ II R (I) and R0 0RX x 3 -Qc; 1 Q O 0 X X F 11/ m u 6 115 G2 wherein R represents a loweralkyl group, an aryl group, an aralkyl group, an acyl group or an aroylgroup; and

X represents a hydrogen atom, a halogen atom, an

alkyl group or a nitro group.

2. The pressure-sensitive copy system of claim 1 wherein,

R represents a lower alkyl group, an aryl group, a benzyl group, a loweracyl group or a benzoyl group; and

X represents a hydrogen atom, a chlorine atom, a

bromine atom, an alkyl group or a nitro group.

3. The pressure-sensitive copy system of claim 1 wherein R is methyl andX is hydrogen, said compounds being trans 3,7-bis[3',6-dimethoxy-9-spiroxanthyl]pyromellitide and cis 3,5-bis[3,6-dimethoxy-9'-spiroxanthyl]pyromellitide.

4. The pressure-sensitive copy system of claim 1 wherein R is methyl andX is methyl, said compounds being trans 3,7-bis[4',5-dimethyl3',6'-dimethoxy-9- 12 spiroxanthyl]pyrome1litide and cis 3,5-bis[4',5'-dimethyl-3',6-dimethoxy-9'-spiroxanthyl]pyrome1litide.

5. The pressure-sensitive copy system of claim 1 wherein R is methyl andX is chlorine, said compounds being trans3,7-bis[2,7'-dichloro-3,6'-dimethoxy-9'- spiroxanthyl]pyromellitide andcis 3,5-bis[2,7'- dichloro-3 ,6 -dimethoxy-9'-spiroxanthyl]pyromellitide.

6. The pressure-sensitive copy system of claim 1 wherein R is benzyl andX is hydrogen, said compounds being trans 3,7-bis[3,6'-dibenzyloxy-9'-spiroxanthyl]- pyromellitide and cis3,5-bis[3',6'-dibenzyloxy-9'- spiroxanthyl]pyromel1itide.

7. The pressure-sensitive copy system of claim 1 wherein R is acetyl andX is hydrogen, said compounds being trans 3 ,7-bis[ 3 ,6' -diacetoxy-9'-spiroxanthyl] pyromellitide and cis 3,5-bis[3',6'-diacetoxy-9'-spiroxanthyl]pyromellitide.

8. The pressure-sensitive copy system of claim 1 wherein R is butyryland X is hydrogen, said cornpounds being trans3,7-bis[3,6'-dibutyroxy-9'- spiroxanthyl]pyromellitide and cis3,5-bis[3,6- dibutyroxy-9-spiroxanthyl]pyromellitide.

9. The pressure-sensitive copy system of claim 1 wherein R is benzoylandX is hydrogen, said compounds being trans 3,7-bis[3',6-dibenzoxy-9'-spiroxanthyl]pyromellitide and cis 3,5-bis[3,6'-dibenzoxy-9-spiroxanthyl]pyromellitide.

10. The pressure-sensitive copy system of claim 1 wherein saidmicrocapsules also contain at least one blue imaging chromogeniccompound.

11. The pressure-sensitive copy system of claim 1 wherein saidmicrocapsules also contain Crystal Violet Lactone and Benzoyl LeucoMethylene Blue.

12. The pressure-sensitive copy system of claim 11 wherein saidmicrocapsules additionally contain 7,7- bis(3-diethylaminofluoran) and7,7'-isopropylidenebis( 3-diethylaminofluoran).

2. The pressure-sensitive copy system of claim 1 wherein, R represents alower alkyl group, an aryl group, a benzyl group, a lower acyl group ora benzoyl group; and X represents a hydrogen atom, a chlorine atom, abromine atom, an alkyl group or a nitro group.
 3. The pressure-sensitivecopy system of claim 1 wherein R is methyl and X is hydrogen, saidcompounds being trans 3,7-bis(3'',6''-dimethoxy-9''-spiroxanthyl)pyromellitide and cis3,5-bis(3'',6''-dimethoxy-9''-spiroxanthyl)pyromellitide.
 4. Thepressure-sensitive copy system of claim 1 wherein R is methyl and X ismethyl, said compounds being trans3,7-bis(4'',5''-dimethyl-3'',6''-dimethoxy-9''-spiroxanthyl)pyromellitideand cis 3,5-bis(4'',5''-dimethyl-3'',6''-dimethoxy-9''-spiroxanthyl)pyromellitide.5. The pressure-sensitive copy system of claim 1 wherein R is methyl andX is chlorine, said compounds being trans 3,7-bis(2,7''-dichloro-3'',6''-dimethoxy-9''-spiroxanthyl)pyromellitide and cis3,5-bis(2'',7''-dichloro-3'',6''-dimethoxy-9''-spiroxanthyl)pyromellitide.6. The pressure-sensitive copy system of claim 1 wherein R is benzyl andX is hydrogen, said compounds being trans 3,7-bis(3'',6''-dibenzyloxy-9''-spiroxanthyl)pyromellitide and cis 3,5-bis(3'',6''-dibenzyloxy-9''-spiroxanthyl)pyromellitide.
 7. Thepressure-sensitive copy system of claim 1 wherein R is acetyl and X ishydrogen, said compounds being trans 3,7-bis(3'',6''-diacetoxy-9''-spiroxanthyl)pyromellitide and cis3,5-bis(3'',6''-diacetoxy-9''-spiroxanthyl)pyromellitide.
 8. Thepressure-sensitive copy system of claim 1 wherein R is butyryl and X ishydrogen, said compounds being trans 3,7-bis(3'',6''-dibutyroxy-9''-spiroxanthyl)pyromellitide and cis 3,5-bis(3'',6''-dibutyroxy-9''-spiroxanthyl)pyromellitide.
 9. The pressure-sensitivecopy system of claim 1 wherein R is benzoyl and X is hydrogen, saidcompounds being trans 3,7-bis(3'',6''-dibenzoxy-9''-spiroxanthyl)pyromellitide and cis3,5-bis(3'',6''-dibenzoxy-9''-spiroxanthyl)pyromellitide.
 10. Thepressure-sensitive copy system of claim 1 wherein said microcapsulesalso contain at least one blue imaging chromogenic compound.
 11. Thepressure-sensitive copy system of claim 1 wherein said microcapsulesalso contain Crystal Violet Lactone and Benzoyl Leuco Methylene Blue.12. The pressure-sensitive copy system of claim 11 wherein saidmicrocapsules additionally contain 7,7''-bis(3-diethylaminofluoran) and7,7''-isopropylidene-bis(3-diethylaminofluoran).